1. Field of the Invention
The present invention relates generally to the field of electronic circuits for surge suppression, and more particularly to a circuit for diverting surges and transient impulses away from sensitive electronic equipment.
2. Description of the Related Art
Surge suppression circuits can be used to protect electronic equipment from voltage surges caused by lightning strikes, switching surges, transients, noise, incorrect connections, and other abnormal conditions or malfunctions. The electronic equipment is extremely susceptible to damage and destruction by very short duration transient voltage spikes. For example, these transient voltage spikes can have durations of about 28 microseconds, peak voltages of about 6,000 volts and peak follow currents of about 3,000 amperes. Even though these transient voltage spikes are generally of short duration, the ultimate effect can result in severe damage to the electronic equipment.
One example of a surge suppression circuit for providing transient voltage surge suppression is shown schematically in FIG. 1. The surge suppression circuit 100 includes a gas tube 102 connected across a signal conductor 104 and a shield conductor 106 of a coaxial cable 108. The shield conductor 106 is coupled directly to ground. If the voltage across the signal conductor 104 exceeds a predetermined level, the gas in the gas tube 102 is ionized, permitting current to flow between the two electrodes inside the gas tube 102. Therefore, when a voltage surge across the signal conductor 104 exceeds the level at which the ionized gas current pathway forms, the voltage is clamped at the ionization voltage of the gas tube 102. During normal operation, the surge suppression circuit 100 passes dc signals, low frequency signals and high frequency signals. During a surge condition, the leading portion of the voltage surge can pass to the electronic equipment because the gas tube 102 does not fire until after the leading portion has traveled past the gas tube 102. Therefore, the gas tube 102 is unable to divert the leading portion of the surge.
One drawback of the surge suppression circuit 100 is its inability to divert the leading portion of the surge, while passing direct current, high frequency rf signals and low frequency signals.